| Abstract: | The aim of this study was to determine if algal products rich in DHA or EPA are able to completely replace fish oil in microdiets for marine fish juveniles, Japanese flounder Paralichthys olivaceus. To address the problem, an 11-d feeding experiment was carried out on 18-day old juveniles. The experimental subjects were fed with five groups of isolipidic and isoenergetic microdiets that were control group with fish oil (FO), 50% replacement group by mixed Schizochytrium sp., Nannochloropsis sp. and olive oil (M50), 100% replacement group (M100), 100% replacement group by Schizochytrium sp. and olive oil (S100), and 100% replacement group by Nannochloropsis sp. and olive oil (N100). The results showed that there were no significant effects of fish oil replacement with microalgae on growth. The groups containing Schizochytrium sp. (M50, M100 and S100) had higher survival rates than FO and N100 groups. No changes in the major fatty acid compositions of juveniles were observed with the replacement of fish oil by microalgae. In addition, Pearson correlation analysis showed that the percentage content of C14:0, C16:1n-7, C18:2n-6, C20:0, C18:3n-3, C22:0, C20:4n-3, EPA, C22:5n-6 and DHA in juveniles were significantly and positively correlative to those in diets (P<0.05). The same correlations were also observed for total saturated, monounsaturated and n-3 polyunsaturated fatty acids, and DHA/EPA ratio. In conclusion, fish oil replacement with microalgae as lipid sources can fully satisfy the growth and development in juvenile flounder, and fatty acids in microalgae can be effectively digested and absorbed. Furthermore, the addition of microalgae in diets enhanced the DHA content and DHA/EPA ratio in juveniles, and hence improved the survival. Therefore, the fish oil replacement with microalgae in the culture of Japanese flounder juveniles is feasible. This study will be helpful and suggestive for screening new lipid sources to replace strained fish oil resource. |
